Tigers chairman Assem Allam has backed the verdict of vice-chairman and son Ehab Allam to dispose of Barmby's services earlier this month.
Barmby was initially suspended on April 30 over comments made about the Championship club's finances and a lack of funds made available to strengthen during the January transfer window.
It was announced on May 8 that Barmby had been sacked after six months in charge of his hometown outfit, a decision the 38-year-old subsequently appealed.
But that has been rejected by Assem Allam following a hearing between him and Barmby.
A full statement from Assem Allam on the Hull Daily Mail website read: "Having heard Nick Barmby's internal appeal and following a full review of the facts during a detailed and thorough meeting with him, I have decided to uphold the vice chairman's decision to dismiss Nick for the reasons previously stated."
Barmby said in a statement released via the League Managers Association: "It goes without saying that I am very disappointed that there wasn’t a favourable outcome to my appeal against my dismissal as manager of Hull City FC.
"I was surprised that the club did not appoint an independent person to hear the appeal and I am now considering the outcome in detail and will consult with the LMA’s legal team before deciding on any further action.
"Whatever the future holds, I want to reiterate my thanks to the fans, players and staff for the support they gave me during my seven years service to the club. I sincerely hope that next season brings success both on and off the field."